kotlin-stdlib / kotlin.collections / reduceIndexedOrNull

reduceIndexedOrNull

Common
JVM
JS
Native
1.4
inline fun <S, T : S> Array<out T>.reduceIndexedOrNull(
    operation: (index: Int, acc: S, T) -> S
): S?
(source)
inline fun ByteArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Byte, Byte) -> Byte
): Byte?
(source)
inline fun ShortArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Short, Short) -> Short
): Short?
(source)
inline fun IntArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Int, Int) -> Int
): Int?
(source)
inline fun LongArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Long, Long) -> Long
): Long?
(source)
inline fun FloatArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Float, Float) -> Float
): Float?
(source)
inline fun DoubleArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Double, Double) -> Double
): Double?
(source)
inline fun BooleanArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Boolean, Boolean) -> Boolean
): Boolean?
(source)
inline fun CharArray.reduceIndexedOrNull(
    operation: (index: Int, acc: Char, Char) -> Char
): Char?
(source)
@ExperimentalUnsignedTypes inline fun UIntArray.reduceIndexedOrNull(
    operation: (index: Int, acc: UInt, UInt) -> UInt
): UInt?
(source)
@ExperimentalUnsignedTypes inline fun ULongArray.reduceIndexedOrNull(
    operation: (index: Int, acc: ULong, ULong) -> ULong
): ULong?
(source)
@ExperimentalUnsignedTypes inline fun UByteArray.reduceIndexedOrNull(
    operation: (index: Int, acc: UByte, UByte) -> UByte
): UByte?
(source)
@ExperimentalUnsignedTypes inline fun UShortArray.reduceIndexedOrNull(
    operation: (index: Int, acc: UShort, UShort) -> UShort
): UShort?
(source)

Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original array.

Returns null if the array is empty.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceOrNull { acc, string -> acc + string }) // abcd
println(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }) // ab1c2d3

println(emptyList<String>().reduceOrNull { _, _ -> "" }) // null
//sampleEnd
}

Parameters

operation - function that takes the index of an element, current accumulator value and the element itself, and calculates the next accumulator value.

Common
JVM
JS
Native
1.4
inline fun <S, T : S> Iterable<T>.reduceIndexedOrNull(
    operation: (index: Int, acc: S, T) -> S
): S?
(source)

Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original collection.

Returns null if the collection is empty.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceOrNull { acc, string -> acc + string }) // abcd
println(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }) // ab1c2d3

println(emptyList<String>().reduceOrNull { _, _ -> "" }) // null
//sampleEnd
}

Parameters

operation - function that takes the index of an element, current accumulator value and the element itself, and calculates the next accumulator value.